1. Field of the Invention
The present invention generally relates to a liquid ink composition and a method of producing the composition. More specifically, the present invention relates to a liquid ink composition and a method for producing an ink composition that is capable of maintaining good characteristics and dissolves or inhibits the formation of ink clots during long term storage by adding a metal salt as a storage stabilizer to the ink composition.
2. Description of the Related Art
Liquid inks are widely used in offset, rotogravure, and ink jet printers and in electrophotographic image forming apparatuses. In the electrophotographic image forming apparatuses, such as copying machines, laser printers, and facsimile machines, liquid inks are used as the liquid toner or developer. Generally, the electrophotographic process includes forming a latent electrostatic image on a charged photoconductor by exposing the photoconductor to radiation according to a predetermined image pattern, contacting the photoconductor with a liquid developer to develop the image, and transferring the developed image onto the liquid developer receiving medium. The image transfer may be performed directly, or indirectly through an intermediate transport member. The developed image is fused permanently onto the receiving medium by heat and/or pressure.
The liquid toners may be classified into two types: a liquid toner generally prepared using general commercial resins and an organosol toner generally prepared using organosols. The organosol toner includes organosols added to a toner acting as a dispersant as well as a binder. U.S. Pat. No. 4,925,766 and U.S. Pat. No. 4,978,598 disclose a liquid electrophotographic toner including the organosol, and a liquid electrophotographic toner preparation method, respectively. As disclosed in these patents, the organosol toner is generally prepared by preparing a (co)polymeric graft stabilizer, preparing the organosol using the (co)polymeric graft stabilizer, and mixing and milling the organosol, the colorant, and additives.
The prepared organosol toner includes stabilized and charged toner particles having a diameter in the range of 0.1 to 5 μm so as to be used to produce a high-resolution image.
Meanwhile, the liquid ink has to be uniformly dispersed to produce a clear image when used in the image forming apparatus. Otherwise, clots may be formed in the inks and the development and the transfer of the image may not be carried out smoothly, thereby interfering with the production of a desired image.
The liquid ink also has to maintain dispersibility after a long storage life taking into consideration the storage time spent before the product is purchased and the actual usage time of the product.
However, while providing the high-resolution image, the organosol toner has shortcomings during the storage. To prepare the organosol toner, the organosol, the colorant, and the charge control agent are put into a carrier liquid and milled by applying a physical force using a milling apparatus at a predetermined temperature. The organosol serves as the dispersant to combine the colorant, the charge control agent, and the additional agents, thus forming the toner particles. For a short period of time at normal temperature, the prepared toner does not generate a considerable amount of the clots of the toner particles. Even if the toner particles is clotted and deposited, it is in small amount and can be dispersed through a simple physical method such as by shaking.
During long term storage and at high temperature, especially at temperatures above the glass transition temperature of an organosol core, the toner particles may combine with each other and be deposited, forming a separate layer in the carrier liquid. Once the toner particles clot and form a separate layer and sediment in the carrier liquid, it is difficult to disperse to the original dispersed state even with excessive physical force. In actual use, it is inevitable that the liquid toner will be stored for a long time. Furthermore, the requirement for high-temperatures to fix the image affects the liquid toner that is stored in the image forming apparatus.
The non-dispersed toner having sediments of the toner particles does not smoothly flow into a developing apparatus, and the printing may not be properly performed. Even if the image is printed, it is difficult to produce a clear image since the liquid toner particles are not completely dispersed.
Accordingly, even in the liquid ink having the organosol as the dispersant to disperse the ink particles, the quality of the liquid ink is not guaranteed if the liquid ink is exposed to high temperatures during long term storage. As a result, there is a need for a liquid ink having an organosol that is stable during long term storage and maintains a uniform quality.